There are two main objectives of the proposed research. The first is to gain more insight into the nature of the metabolic events that are triggered by the interaction of growth hormone (GH) with its receptors and that lead to its well characterized effects on protein, amino acid and carbohydrate metabolism. Using the isolated diaphragm of the hypophysectomized rat, a variety of probes (antibodies against GH, theophylline, microfilament and microtubule modifiers, calcium ionophores) will be employed in an attempt to identify those aspects of cellular function that are involved in transducing the GH-receptor interaction into stimulatory effects on protein synthesis and the membrane transport of amino acids and monosaccharides. The second major objective is to carry out a detailed analysis of the relationship between the level of GH in the blood of the rat and the activity of various metabolic processes influenced by the hormone. Using hypophysectomized rats bearing indwelling aortic cannulae, various levels and patterns of circulating GH within the range seen normally will be achieved by infusion of rat GH (rGH) via the cannula. The acute effects of these changes in circulating rGH on labeled amino acid incorporation into plasma protein, and the steady-state distribution of non-metabolizable amino acids and sugars will be studied. The goal is to establish whether or not there is coupling between episodes of enhanced GH secretion and metabolic activity.